1. Field of the Invention
The present invention relates to a visible light communication apparatus that performs visible light communication by using a modulation signal for changing an emitting state of visible light, and a visible light communication method that outputs an operation state of an electric appliance.
2. Description of Related Art
When displaying states of various electric appliances including a communication apparatus, various devices are used including a basic spot-like display such as an LED or a lamp (hereinafter referred to as a “spot-display device”) and a 2D-display device such as a CRT display and an LCD (hereinafter referred to as a “panel display device”).
When displaying a state by using a spot-display device, a plurality of states are distinctively displayed by luminous timings such as continuous lightings, lights-out and blinks, or luminous colors. Providing a spot-display device, which is capable of displaying various states, error areas and the like, makes it possible to indicate various conditions of an electric appliance including whether the electric appliance is on or off and whether an error has occurred or not.
However, there is a limit to the number of states that a spot-display device can display, and it is usually difficult to display a detailed state. Further, since it is necessary to provide different spot-display devices for displaying various items in accordance with the device types and contents to be displayed (e.g., operation/non-operation of an electric appliance, states of device components, states of connected devices), it is difficult to display all the states of device types and contents when there is a physical limit to areas where spot-display devices can be installed. Moreover, users may have a hard time understanding display contents since various states are specified by continuous lightings, lights-out, blinks, etc.
When displaying a state by a panel display device, on the other hand, letters and the like can be displayed, thus achieving a further detailed display. It is also possible to display troubleshooting procedures suitable for various situations when abnormal states or the like occur. However, some electric appliances are difficult to install such panel display devices due to physical and limitations. Further, in some cases, depending on where such electrical appliances are installed, it may be hard for users to view the panel display devices on those appliances directly, thereby hindering users' recognition of the displayed contents themselves.
In general, a communication apparatus such as a power line carrier communication modem displays a communication state and the like by using a spot-display device. For instance, the data communication modem apparatus disclosed in Japanese Patent Laid-Open Publication H5-75672 uses one LED to display one of the following states: performing no communication, being connected to the line, and transmitting data. The wireless communication apparatus disclosed in Japanese Patent Laid-Open Publication 2003-134131 includes a state display including a plurality of colors of LEDs for displaying operation states. Therefore, such a communication apparatus is not capable of displaying detailed states including whether the communication apparatus is being connected or not, a state of a connected communication apparatus, and a state of a transmission line.
In recent years, an information communication method called visible light communication has been proposed (Refer to URL: http://www.vlcc.net/). Visible light communication performs communication using light that is perceivable by the human eye (visible light). In visible light communication, a visible light emitting device such as an LED undergoes high-speed modulation for data transmission. Since a visible light zone is safe to human, it can be transmitted while maintaining a high power level of a few watts used for lighting. Therefore, simply adding communication functions to a lighting device or the like can easily build a wireless environment. Further, there are suggestions of lighting optical communication utilizing illuminated light sources, and ITS visible light communication utilizing a signal or automobile light.